1. Field of Invention
The present invention relates to a power switch device. More particularly, the present invention relates to a power switch device with a self-biasing circuit.
2. Description of Related Art
With the high demand on portable electronic devices, power management is an important issue for maintaining operation time. Generally, the portable electronic device integrates a lot of components and those components may be powered by different power sources.
FIG. 1 shows a conventional power switch device including switches S11 and S12. First terminals of the switches S11 and S12 receive input voltages Vin11 and Vin12 respectively. Second terminals of the switches S11 and S12 are coupled together for outputting a power source Vpp1. Two non-overlapping enable signals SEN11 and SEN12 are used for controlling the voltage switch. The switch S11 is turned on under control of the enable signal SEN11 while at the same time the switch S12 is turned off under control of the enable signal SEN12; and the switch S11 is turned off under control of the enable signal SEN11 while at the same time the switch S12 is turned on under control of the enable signal SEN12. When the switch S11 is turned on and the switch S12 is turned off, the power source Vpp1 takes in the input voltage Vin 11. Similarly, when the switch S12 is turned on and the switch S11 is turned off, the power source Vpp1 takes in the input voltage Vin12. The power source Vpp1 is switched as either of the input voltages Vin11 and Vin12. Therefore, under control of the enable signal SEN11 and SEN12, the conventional power switch device supplies the power source Vpp1 with different voltage values.
However, if the power source Vpp1 is used in a high voltage application, the power switch device has to be manufactured by high voltage manufacturing process. For example, if the power source Vpp1 is switched as either one of 1.8V and 7V, a high voltage manufacturing process suitable for 7V power source is applied to make the power switch device. But the resultant power switch device by high voltage manufacturing process has large circuit size and severe power consumption.